Sediment behavior controls equilibrium width of subglacial channels

TitleSediment behavior controls equilibrium width of subglacial channels
Publication TypeJournal Article
Year of Publication2017
AuthorsDamsgaard A., Suckale J., Piotrowski J.A, Houssais M., Siegfried M.R, Fricker H.A
JournalJournal of Glaciology
Volume63
Pagination1034-1048
Date Published2017/12
Type of ArticleArticle
ISBN Number0022-1430
Accession NumberWOS:000418852500009
Keywordsantarctic ice stream; basal mechanics; bed; beneath glaciers; deformation; discrete particle simulation; glacial tills; glacier hydrology; granular-materials; numerical experiments; sediments; subglacial; subglacial processes; tidewater glaciers; water-pressure; west antarctica
Abstract

Flow-frictional resistance at the base of glaciers and ice sheets is strongly linked to subglacial water pressure. Understanding the physical mechanisms that govern meltwater fluxes in subglacial channels is hence critical for constraining variations in ice flow. Previous mathematical descriptions of soft-bed subglacial channels assume a viscous till rheology, which is inconsistent with laboratory data and the majority of field studies. Here, we use a grain-scale numerical formulation coupled to pore-water dynamics to analyze the structural stability of channels carved into soft beds. Contrary to the soft-bed channel models assuming viscous till rheology, we show that the flanks of till channels can support substantial ice loads without creep closure of the channel, because the sediment has finite frictional strength. Increased normal stress on the channel flanks causes plastic failure of the sediment, and the channel rapidly shrinks to increase the ice-bed contact area. We derive a new parameterization for subglacial channelized flow on soft beds and show that channel dynamics are dominated by fluvial erosion and deposition processes with thresholds linked to the plastic rheology of subglacial tills. We infer that the described limits to channel size may cause subglacial drainage to arrange in networks of multiple closely spaced channels.

DOI10.1017/jog.2017.71
Short TitleJ. Glaciol.
Student Publication: 
No